1. Technical Field
The present invention relates to an image capture apparatus, an image processing apparatus, an image processing method, a program for the image processing method, and a recording medium that records therein the program for the image processing method, which are adaptable to, for example, digital still cameras. According to the invention, a pixel value of each interest pixel is converted into a pixel value for noise removal based on a processing reference pixel value having a unified color signal component in each interest pixel to remove noise therefrom, and then the pixel value is reversely converted into the original pixel value to effectively prevent image quality degradation, whereby color noise included in raw data can be removed.
2. Background Art
In conventional digital still cameras, after raw data serially acquired in a pixel array of an imaging device is demosaiced and a full color image is generated thereby, the data is converted to image data of a luminance signal and a color difference signal and recorded on a recording medium. It is known that noise of such a color image is classified into luminance noise, which is the noise of the luminance signal component, and color noise, which is the noise of the color signal component exclusive of the luminance signal component. And an image quality can be significantly improved by removing the color noise.
In regard to digital still cameras, in Japanese Unexamined Patent Application Publication No. 2005-311455, a method is proposed in which a peripheral pixel appropriate for a noise reduction process is selected, and the noise reduction process is executed by use of the selected peripheral pixel, thereby to efficiently remove the noise in the stage of the raw data.
Further, in Japanese Unexamined Patent Application Publication No. 2004-221838, a method of accurately regenerating an edge in the manner that, in a demosaicing process or the like, an interpolation calculation process of a pixel value of an interest pixel is executed by use of pixel values in a predetermined range present along the extensional direction of the edge.
By the way, when color noise is removed in the raw data stage, there is a problem that even the luminance signal component is affected, and hence even the luminance value of each color signal is changed. As a consequence, a case can occur in which an edge portion and like are displayed in an incorrect color, thereby leading to significant deterioration in image quality.
As one method for solving the problem, it can be considered that noise is removed in the stage of the luminance signal and the color difference signal. According to the method, it can be considered that the color noise can be removed without affecting the luminance signal.
However, in this method, since the demosaicing process is executed in the state where the data is contaminated with noise, a problem takes place in that the demosaicing process is affected when there is a significant amount of noise contamination. More specifically, in the case where, for example, an edge is regenerated by the demosaicing process or the like in accordance with the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-221838, a case can occur in which the edge is regenerated incorrectly due to noise, the edge portion and the like are displayed in the incorrect color and color noise rather occurs to the extent of significantly degrading image quality. Further, a problem can occur in that the noise characteristics are intricately changed through the series of processes from the raw data stage in the stages of the luminance signal and the color difference signal, consequently making it impossible to remove the color noise. Further, there is a case where the configuration of a noise removing circuit cannot be provided due to configurational restrictions of a signal processing circuit and the like. In this case, there is a problem in that the method cannot be adapted.